I'm thinking he (or more likely, his agent) said it to coax out an offer from the Marlins - otherwise I don't think the Marlins were even thinking about doing it. It works to his benefit. He gets an extra offer and kind of sees where they're at (to make it a starting point as far as potential deals), then basically lets media and the fans view it as "cheap Marlins again" and that it just didn't work out (after all, he said he wanted to stay here - totally genuine and definitely not a strategy), then tests the FA market and gets any other team with bigger pockets to offer that 1 more year.
I think he's delusional if he really thinks he's even close to guaranteeing getting 5 to 6 Million or higher next time around in the draft, let alone now. Watson ain't getting #4 slot money. Sign now, or miss the chance to get $4.5 Million, big boy.